This Review provides an introduction to the compensation of loss and amplification of surface plasmons in waveguides and resonators. Future challenges, including how to overcome the large losses present in plasmonic systems that offer strong electromagnetic confinement, are also discussed.

Surface plasmon–polariton amplifiers and lasers

Nanocrystalline Ln 3 + -doped YF 3 phosphors have been synthesized via a facile sonochemistry-assisted hydrothermal route. YF 3 nanoparticles are demonstrated to be a good host material for different lanthanides. Varying the dopants leads to different optical properties. In particular, the feasibility of inducing red, green, and especially blue emission in the Yb 3 + /Er 3 + co-doped YF 3 sample by up-conversion excitation in the near-infrared region is demonstrated. Such unusually strong 411 nm blue up-conversion emission has seldom been reported in other Yb 3 + /Er 3 + -doped systems. The up-conversion mechanisms have been analyzed.

Down/Up Conversion in Ln3+-Doped YF3 Nanocrystals

Erbium-doped fiber devices have been extraordinarily successful due to their broad optical gain around 1.5–1.6 μm. Er-doped fiber amplifiers enable efficient, stable amplification of high-speed, wavelength-division-multiplexed signals, thus continue to dominate as part of the backbone of longhaul telecommunications networks. At the same time, Er-doped fiber lasers see many applications in telecommunications as well as in biomedical and sensing environments. Over the last 20 years significant efforts have been made to bring these advantages to the chip level. Device integration decreases the overall size and cost and potentially allows for the combination of many functions on a single tiny chip. Besides technological issues connected to the shorter device lengths and correspondingly higher Er concentrations required for high gain, the choice of appropriate host material as well as many design issues come into play in such devices. In this contribution the important developments in the field of Er-doped integrated waveguide amplifiers and lasers are reviewed and current and future potential applications are explored. The vision of integrating such Er-doped gain devices with other, passive materials platforms, such as silicon photonics, is discussed.

Erbium-doped integrated waveguide amplifiers and lasers

In this Full Paper, a water/alcohol/oleic acid system was developed to prepare NaYF 4 nanocrystals with predictable size, shape and phase. The structural and kinetic factors that govern the phase and shape evolution of NaYF 4 nanocrystals have been carefully studied, and the influence of NaF to Y 3+ ratio, reaction time and temperature on the phase and shape evolution of the as-prepared NaYF 4 samples was systematically investigated and discussed. It was found that the NaF to Y 3+ ratio was responsible for the shape evolution while temperature and reaction time was the key for the phase control of the NaYF 4 nanocrystals. This study would be suggestive for the precisely controlled growth of inorganic nanocrystals, especially for those usually crystallizing in diverse crystal structures.

Synthesis of NaYF4 Nanocrystals with Predictable Phase and Shape

Three different broadband sensitization concepts for optically active erbium ions are reviewed: 1) silicon nanocrystals, with absorption over the full visible spectrum, efficiently couple their excitonic energy to Er3+, 2) silver-related defect states in sodalime silicate glass have absorption in the blue and transfer energy to Er3+, and 3) organic cage complexes coordinated with well-chosen chromophores serve as broadband sensitizers in the visible. Energy transfer rates, efficiencies, and limiting factors are addressed for each of these sensitizers. Implications of the use of strong sensitizers for planar waveguide design are illustrated by using a model for the sensitizing effect of ytterbium.

Broadband sensitizers for erbium-doped planar optical amplifiers: review

Erbium-doped multicomponent phosphate glass waveguides were deposited by rf sputtering techniques. The Er concentration was 5.3×1020 cm−3. By pumping the waveguide at 980 nm with a power of ∼21 mW, a net optical gain of 4.1 dB at 1.535 μm was achieved. This high gain per unit length at low pump power could be achieved because the Er–Er cooperative upconversion interactions in this heavily Er-doped phosphate glass are very weak [the upconversion coefficient is (2.0±0.5)×10−18 cm3/s], presumably due to the homogeneous distribution of Er in the glass and due to the high optical mode confinement in the waveguide which leads to high pump power density at low pump power.

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de H Henk Waal

Papers

Erbium-doped phosphate glass waveguide on silicon with 4.1 dB/cm gain at 1.535 µm